The present invention is directed, in general, to optical electronics, and more specifically, to an optical modulator and method of manufacture thereof.
Micro-electromechanical system (xe2x80x9cMEMSxe2x80x9d) optical modulators have been shown highly desirable for use in flattening and equalizing the gain spectrum of an optically amplified system. One such example of a MEMS optical modulator is disclosed in U.S. Pat. No. 5,943,158, entitled xe2x80x9cMicro-Mechanical, Anti-Reflection, Switched Optical Modulator Array and Fabrication Method,xe2x80x9d by Ford, et al., which is hereby incorporated by reference in its entirety.
An optical modulator, such as that disclosed in Ford et al., generally creates and judiciously modulates a controlled reflectivity surface that is put in the path of an optical signal, such as a spectrally dispersed signal. As a result, the optical modulator selectively reflects, and thereby attenuates, a desired spectral amplitude. The reflectivity, and hence the attenuation, of the optical modulator may be set by controlling the distance, also called an xe2x80x9cairgap thicknessxe2x80x9d or a xe2x80x9cgap layerxe2x80x9d, between a suspended dielectric film or xe2x80x9cmembranexe2x80x9d (perhaps with an upper and lower optically active polysilicon film attached) and a reflective silicon substrate. The amplitude of the airgap thickness or gap layer may in turn be a function of an attractive force created by an electromagnetic field developed between electrodes disposed proximate the membrane and conductors disposed upon a reflective silicon substrate or the reflective silicon substrate itself.
A nagging problem with optical modulators of the past, however, is the need to provide optical feedback to control the position of the membrane while drive electrodes associated with the membrane undergo a voltage bias. For instance, among other things, gas in the space or gap (i.e., the xe2x80x9cairgapxe2x80x9d) between the membrane and the silicon substrate can ionize due to the applied electromagnetic field. As a result of this ionization, electrostatic charges may build up on the membrane itself, thereby changing the electromagnetic force between the membrane and the silicon substrate. The change in electromagnetic force then, in turn, may disadvantageously lead to a change in the membrane position, which ultimately may lead to an undesirable change in the constant of reflectivity, and hence an undesirable change in reflectivity.
Presently, however, the only system for providing feedback to control the reflectivity of the optical modulator is to monitor the output optical signal at specific wavelengths, and then to compare this signal to the desired signal level. Computer processor control may then be used to set the drive voltages at the electrodes to correct for deviations. Unfortunately, the optical monitors for providing this feedback signal are expensive, add optical loss, and complicate the optical design, even should such problems as the charge buildup on the membrane be resolved.
Accordingly, what is needed in the art is a system that better monitors the position of the membrane of the optical modulator that overcomes the deficiencies associated with the prior art.
To address the above-discussed deficiencies of the prior art, the present invention provides an optical modulator having an optical modulator window coupled to a substrate and a method of manufacture thereof. In one embodiment, the optical modulator includes at least one drive electrode that adjusts a portion of the optical modulator window to attenuate light passing therethrough. The optical modulator further includes a sense element configured to measure a characteristic associated with the optical modulator window.
In another aspect, the present invention provides an optical modulator that includes a substrate and a gap layer located over the substrate. The optical modulator also includes a modulator region located over the gap layer. The optical modulator still further includes a drive electrode located proximate to the modulator region and a sense element located proximate to the modulator region.
In yet another aspect, the present invention a method of manufacturing an optical modulator over a substrate. The method includes forming a gap layer over the substrate and a modulator region over the gap layer. The method also includes forming a drive electrode over the modulator region and forming a sense element over the modulator region proximate the drive electrode.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.